In recent years, the utilization of a virtual storage system capable of achieving unrestricted capacity and configuration thereof regardless of the volume configuration and capacity of a physical storage system has been progressing. In the virtual storage system, a virtual volume is provided as a management unit of a storage system.
The virtual storage system multiplexes, assuming that failures occur in a storage device that stores data, a logical unit number (LUN) that constitutes the virtual volume to perform mirroring of data.
The virtual storage system performs the mirroring of data to continue I/O via a LUN other than a LUN associated with the storage device in which failures occur, thus improving the availability thereof as a storage.
Here, there exists a conventional technique that allows a user to select, out of a plurality of volume groups, only a part of the volume groups as a target of mirroring, thus specifying a fail-back operation only to specific volume groups by the user.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-328785
Patent Document 2: Japanese Laid-open Patent Publication No. 2007-535763
When the mirroring is performed in an active/active virtual storage system, there exists a drawback that data mismatching may occur in mirroring. Here, the “active/active” means a system in which an access request from a business server that uses a virtual storage system can be received by any storage device in the virtual storage system. On the other hand, a system in which the access request from the business server is received only by an active storage device is referred to as “active/standby”.
The active/active system requires complicated processing. However, the active/active system has advantages such as load distribution or quick recovery from a failure and hence, there exists a tendency that the use of the active/active virtual storage system increases.
FIG. 10 is a view for explaining a drawback of mirroring in the active/active system. In FIG. 10, each of two nodes 9 illustrated as a node #1 and a node #2 is a storage device that performs mirroring of data, and VDisk indicates a virtual volume.
As illustrated in FIG. 10, a business server 10 requests the node #1 to write data A in the VDisk a (1), and requests the node #2 to write data B in the VDisk a (2). Furthermore, the node #2 writes the data B in an intended disk device 41 in a storage part of the node #1 (3) and thereafter, the node #1 writes the data A in the disk device 41 of the node #1 (4).
Meanwhile, the node #1 writes the data A in the disk device 41 of the node #2 (5) and thereafter, the node #2 writes the data B in an intended disk device 41 in a storage unit of the node #2 (6). In this case, as data written in the VDisk a, while the data A is stored in the disk device 41 of the node #1, the data B is stored in the disk device 41 of the node #2.
In this manner, in the active/active system, all the volumes are accessible from any of nodes 9 in a virtual storage system and hence, the simultaneous writing control of an identical virtual volume may be performed by a plurality of controllers different from each other of the respective nodes 9. A controller that has received a write request performs writing control and mirroring control with respect to a mirror destination. In this case, it is impossible to control the order of writing data in the disk devices 41 allocated to the virtual volume. Accordingly, as described above, there exists the possibility that data are written in different orders between the disk devices arranged in the respective nodes as a mirror source and a mirror destination, and data mismatching occurs in mirroring.